1. Field of the Invention
The present invention relates to a driver's cab for a work vehicle such as a construction machine including a excavator, a farm machine including a tractor, and other industrial machines.
2. Description of the Background Art
The work vehicle includes various kinds such as the construction machine, the farm machine, cargo handling machine, and other such machines however, for example, the excavator in the construction machine is widely used for a civil engineering work accompanying with a segment excavation, a construction foundation work, a building dismantling work or the like. In these works, an operator operates and handles the working machine while seeing forward mainly through a front window from an inner side of the driver's cab. For the driver's cab of the work vehicle in which the work is carried out while seeing mainly forward from the inner side of the driver's cab as mentioned above, it is most desired in view of carrying out the work that a forward view from the front window is wide.
In order to correspond to an improvement in the view, if a width of each of front pillars positioned in both forward sides can be made narrow in view of a structure of the driver's cab, this structure can reduce a presence of the structure blocking the operator's view at a time of working. However, in the work in the construction field having a bad false work such as the work in a slope ground in the case of the excavator, there is a risk that a vehicle body inverts.
Accordingly, it is necessary to obtain a structure in which a deformation in a frame of the driver's cab is small so that the operator within the driver's cab can be protected even when the vehicle body inverts and an inverting load is applied to the driver's cab. As a prior art for intending to strengthen the structure of the driver's cab as mentioned above, there has been known, for example, by Japanese Unexamined Patent Publication No. 11-165660 or Japanese Unexamined Patent Publication No. 11-166247.
In the structure disclosed in Japanese Unexamined Patent Publication No. 11-165660, there is shown a structure in which a frame reinforcing plate connects between right and left side surface frames which are provided with hollow portions by combining a side outer panel constituted by a press member with an inner panel. There is described a matter that a strength of the driver's cab is increased against an inverting load by employing the structure mentioned above. Further, in Japanese Unexamined Patent Publication No. 11-166247, there is shown a structure in which a reinforcing plate separating a hollow portion is assembled in an inner portion of a pillar portion formed by a combination between an inner plate and an outer plate which press mold a frame of the driver's cab, and there is described a matter that a strength of the pillar portion is effectively improved while keeping a shape of the conventional driver's cab, thereby intending to improve a strength of the driver's cab against the inverting load.
However, since both of the prior arts mentioned above correspond to a strengthening countermeasure which attaches importance to a cross sectional structure of the pillar portion, the countermeasure does not achieve a structure which is prepared for the case that an external force is applied to a ceiling portion of the driver's cab from an external portion, for example, from a side surface portion and the case that the external force is applied from a rear side of the ceiling portion.
In accordance with the matter mentioned above, for example, when the great external force is applied to a middle position of the ceiling portion in a longitudinal direction of the driver's cab, the external force is not transmitted well to the pillar at the middle position, so that there is a risk the ceiling portion is largely deformed. In order to achieve a structure which can avoid the matter, it is necessary to reinforce the pillar excessively or it is necessary to arrange an additional pillar in the side of the working machine. Further, when there is generated a matter that the external force is applied to a rear portion of the ceiling of the driver's cab, there is a risk that the ceiling is pressed down to an inner side, in view of the structure which is not prepared for the external force. In any case, because of intending a weight saving of the vehicle body and giving a priority to an improvement of visibility at the time of driving, it is absolutely insufficient to transmit the external force to the pillar in the case that the external force is applied to the ceiling portion due to the inverting load, and it is unavoidable that the deformation of the driver's cab becomes large accompanying therewith. In other words, a risk of the operator is great.